Interaction analysis of a pregnant female uterus and fetus in a vehicle passing a speed bump.

Pregnant vehicle occupants experience relatively large acceleration when the vehicle passes a speed-bump. In this paper, the effect of such sudden acceleration on a pregnant uterus is investigated. A biomechanical model representing the fundamental dynamic behaviors of a pregnant uterus has been developed. The model relates to the 32nd week of gestation when the fetus is in head-down, occipito-anterior position. Considering the drag and squeeze effects of the amniotic fluid, we derive a comprehensive differential equation that represents the interaction of the uterus and fetus. Solving the governing equation, we obtain the system response to different speed-bump excitations. Using the fetal head injury criterion (HIC = 390), we evaluate the model response. Three risk zones (Low, Medium, and High) are introduced, and the effects of excitation characteristics on HIC are investigated. HIC enhances, sub-exponentially, as the excitation amplitude (width) increases (decreases). Three risk-bounds, corresponding to 25%, 75%, and 100% risk of injury, are developed in the "width-amplitude" and the "frequency-amplitude" planes. Considering a typical speed-bump of width and excitation amplitude of 0.5 m and 0.12 m, respectively, the driver should not hit the speed-bump at 42 km/h or more. We advise hitting such speed-bumps under 25 km/h, based on this paper's findings. According to the risk-bounds, the injury risk of an arbitrary speed-bump excitation, at any desired vehicle speed, can be determined. The findings can help to understand how a pregnant uterus and fetus are subjected to risk caused by a vehicle passing a speed-bump and to expand our knowledge to improve safety during pregnancy.

Rigid-bar loading on pregnant uterus and development of pregnant abdominal response corridor based on finite element biomechanical model.

During pregnancy, traumas can threaten maternal and fetal health. Various trauma effects on a pregnant uterus are little investigated. In the present study, a finite element model of a uterus along with a fetus, placenta, amniotic fluid, and two most effective ligament sets is developed. This model allows numerical evaluation of various loading on a pregnant uterus. The model geometry is developed based on CT-scan data and validated using anthropometric data. Applying Ogden hyper-elastic theory, material properties of uterine wall and placenta are developed. After simulating the "rigid-bar" abdominal loading, the impact force and abdominal penetration are investigated. Findings are compared with the experimental abdominal response corridor, previously developed for a nonpregnant abdomen. "Response corridor" denotes a bounded envelope in response space, within which the system responses usually lie. Results show that at low abdominal penetrations (less than 45 mm), the pregnant abdomen response is highly compatible with the nonpregnant case. While, at large penetrations, the pregnant abdomen demonstrates stiffer behavior. The reason must be the existence of a fetus in the model. This reveals that the existing response corridors would not be reliable to be extended for a pregnant abdomen. Hence, response corridor development for a pregnant abdomen is a crucial task. In this study, a new fixed-back rigid-bar loading response corridor is proposed for a pregnant abdomen using the load-penetration behavior of the developed model. This model and response corridor can help to study the pregnant uterus response to environmental loading and investigate the injury risk to the uterus and fetus.